1. Field of the Invention
The present invention relates to a heat accumulator, using latent heat accompanying melting and solidification of a salt hydrate, which is effectively used for a quick-acting heater for an automobile, a quick-acting defroster, a quick-acting heating seat, an engine oil heating device, a hot water supplying device used in a house, or the like.
2. Description of the Related Art
A heat accumulator using latent heat in which heat absorbing and discharging actions accompanying a phase change such as melting, solidification, and the like of a salt hydrate are used is proposed in DE-A1-4244465.
In the technique, Ba(OH).sub.2 .cndot.8H.sub.2 O which is a salt hydrate is used as a heat accumulating medium causing no supercooling. Ba(OH).sub.2 .cndot.8H.sub.2 O absorbs latent heat from the outside in a solid state and liquefies when the melting point is reached. When it solidifies from the liquid state, the absorbed latent heat, for example, 70 cal/g, is discharged to the outside.
By using such a heat accumulating medium, a large amount of the latent heat is obtained and if the latent heat absorbed from the outside is stored into a heat accumulating medium and the heat is discharged when it is needed, it can be effectively used for a quick-acting heater for an automobile, a quick-acting defroster, a quick-acting heating seat, an engine oil heating device, a hot water supplying device used in a house, and the like.
When a distribution of water formed at the time of the melting is not uniform, a phase separation where an unmelted refractory crystal of a high density is deposited at a temperature equal to or larger than a melting point occurs. Since the heat of melting cannot be absorbed by an amount corresponding to the deposited crystal, a heat accumulation density of the heat accumulator is reduced. In order to prevent the phase separation by making the distribution of water forming at the time of the melting uniform, for example, the heat accumulating medium may be mixed with hydrophilic polysaccharide or the like such as xanthin gum as a thickener (see, e.g., Japanese Patent Laid-Open Publication No. 59-53578).
In the heat accumulator such that the heat accumulating medium comprising a salt hydrate is housed in the heat accumulating vessel, however, even if a thickener is added, the distribution of water forming at the time of the melting varies while the heat accumulating medium repeats the melting and the solidification, and the unmelted refractory crystal having a high density is deposited even at a temperature equal to or larger than the melting point. Further, when such a crystal exists, the crystal becomes a core and the unmelted refractory crystal grows while the melting and the solidification are repeated. Since the latent heat cannot be absorbed by an amount corresponding to the crystal, the heat accumulating density of the heat accumulator is reduced.
Since the sensible heat of the thickener is smaller than the latent heat of the heat accumulating medium, when the thickener is added, the heat accumulating density of the heat accumulator is reduced by an amount corresponding to the thickener.